PART 2 This open-label Phase IV study will evaluate the efficacy, safety, pharmacokinetics, pharmacodynamics and immunogenicity of RoActemra/Actemra (tocilizumab) in reduced dose frequency in participants with adequately controlled systemic juvenile idiopathic arthritis who have experienced a laboratory abnormality on twice weekly RoActemra/Actemra dosing, that has since resolved. Participants will receive RoActemra/Actemra 12 mg/kg or 8 mg/kg intravenously every 3 weeks. After 5 consecutive infusions, participants who experience an event of neutropenia, thrombocytopenia or liver enzyme abnormality will move to every 4 weeks RoActemra/Actemra administration. Anticipated time on study treatment is 52 weeks.